#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using pii = pair<int, int>;
#define rep(i, a, b) for (int i = (a); i <= (b); i++)
#define per(i, a, b) for (int i = (a); i >= (b); i--)
#define endl '\n'
const int N = 2e5 + 5;

int n, m;

int main() {
  ios::sync_with_stdio(0), cin.tie(0), cout.tie(0);
  string s;
  cin >> n >> s;
  vector<int> a;
  rep(i, 0, n - 1) if (s[i] == '1') a.push_back(i);
  n = a.size();
  if (!n) {
    cout << 0;
    return 0;
  }
  int mid = a[n / 2];
  ll sum = 0;
  rep(i, 0, n - 1) sum += abs(a[i] - mid);
  mid = n / 2;
  rep(i, 0, n - 1) sum -= abs(i - mid);
  cout << sum;
  return 0;
}